Method of injection molding star-couplers

ABSTRACT

A star-coupler and a method for constructing the star-coupler employing injection molding technology are disclosed. The star-coupler may be constructed from a single injection molded block or a plurality of mating sections, and is supplied with a plurality of input ports and a plurality of output ports. Each input port as well as each output port is connected to at least one channel. The channels are filled with a fiber optical core material and the single block or mating sections are fabricated from fiber optical core material. Alternatively, a separate cladding material may be coated on the surfaces of the block or mating sections which define the channels. Optical signals are guided and confined by the core and cladding material from input ports to output ports along the channels.

This is a continuation of application Ser. No. 07/297,009 filed Jan. 12,1989 now abandoned.

BACKGROUND OF THE INVENTION

The present invention is directed to star-couplers in which a pluralityof optical fibers are connected together. The invention is also directedto methods for making the couplers.

Data transmission over optical fibers offers many significant advantagescompared with metallic conductors, including: long distance transmissionwithout the need for repeaters, immunity from electromagneticinterference, cross-talk and ground loop, high bandwidth capabilities,small size and weight, high degree of intercept security and dielectricisolation, and long term cost reduction. These desirable features ofoptical fibers have strongly stimulated efforts both in fiber optics andin supporting technologies such as fiber optic coupling.

Fiber optic couplers provide for feeding and tapping of optical energy.Fiber optic couplers are widely used in multi-terminal communicationsystems and data buses. In these applications, a common optical pathprovides communication among a plurality of terminals. Typically, eachterminal communicates to every other terminal and provides informationon a time shared basis. The effectiveness of such systems depends oncharacteristics of the optical fibers themselves as well as on thecoupling devices employed to share and distribute information.

A star-coupler is a device which distributes the power on any one ofseveral incoming channels to every one of its outgoing channels.Star-couplers are intended to have minimal insertion losses and asubstantially uniform power distribution over the outgoing channels.Thus, a system employing a star-coupler and a plurality of terminalsrepresents a parallel distribution system.

Star couplers are particularly useful in the field of opticalcommunications for coupling together a plurality of optic fibers to forma network. Several different starcouplers are known. In general, thecouplers have a plurality of incoming channels, a plurality of outgoingchannels and a mixing zone which couples optical signals from any one ofthe incoming channels to all of the outgoing channels. The mixing zonemay comprise optic fibers which are tapered and fused together or waveguides in solid blocks of glass. These glass blocks usually have waveguides specially prepared by ion exchange processes or otherwise, andthe fibers are aligned with the wave guides. The incoming and outgoingchannels are typically bundles of optical fibers. Information in theform of light pulses as signals from any single optical fiber of theinput fiber optic bundle is transmitted via the coupler to each of theoptical fibers in the output fiber optic bundle. Illustrative patentsdescribing these structures include U.S. Pat. Nos. 4,291,940, 4,362,357,4,449,783, 4,484,794, 4,590,619 and 4,653,845.

Unfortunately, the above-mentioned type of starcouplers are generallycostly and difficult to construct.

SUMMARY OF THE INVENTION

We have devised a star-coupler that is made by injection moldingtechniques using optical plastics such as those used in optical fibertechnology. In accordance with our invention, the coupler comprises ablock of plastic or other suitable material that is injection molded toform input and output connectors and a mixing zone. The block is made ofa core and an outer cladding. The core is made of a material having anindex of refraction that is higher than that of the cladding.Advantageously, the core is made of pure polymethylmethacrylate (PMMA)and the cladding is made of fluorinated PMMA. Because the coupler ismade by molding techniques, fabrication costs are relatively lowcompared to those of conventional star-couplers.

The input and output connectors are defined in the injection moldingprocess to have a shape which facilitates their connection toconventional optic fibers and connectors. As a result, the star-couplercan readily be connected to the fibers which it is to couple.

The coupler is injection molded following any one of a number oftechniques. For example, the coupler can be formed by injection moldinga bottom half and a top half with a material that has a refractive indexsimilar to that of the cladding. Channels are defined in the bottomand/or top halves for receiving the core material, the two halves arefitted together with the channels forming a cavity therebetween and thenthe core material is injection molded into the cavity defined betweenthe cladding halves.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects, features and advantages of the invention willbecome more readily apparent from the following detailed description ofa preferred embodiment of the invention in which:

FIG. 1 is a schematic illustration of a 4×4 star-coupler of the presentinvention;

FIG. 2 is a schematic illustration of a second embodiment of a 4×4star-coupler of the present invention;

FIG. 3 is a schematic illustration of a third embodiment of a 4×4star-coupler of the present invention;

FIG. 4 is a perspective view of the top and bottom halves of thecladding of the injection molded coupler of FIG. 1;

FIG. 5 is a modified cross-sectional view along line 5--5 of FIG. 4; and

FIG. 6 is a perspective view of a portion of the injection moldedcoupler of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

As shown schematically in FIG. 1, an illustrative embodiment of theinvention comprises four input ports 12, 14, 16, 18, a mixing channel orzone 20 and four output ports 22, 24, 26, 28. Input ports 12, 14, 16, 18are connected to mixing zone 20 by channels 13, 15, 17, 19,respectively. Mixing zone 20 is connected to ports 22, 24, 26, 28 bychannels 23, 25, 27, 29, respectively.

These channels and the mixing zone propagate optical signals. Thus,light input to any of the input ports will be transmitted to mixingelement 20 where it is then distributed to all of the output ports. Forexample, light input at input port 12 is transmitted by channel 13 tomixing zone 20. Mixing zone 20 then distributes the light from port 12to each of output ports 22, 24, 26, 28 along channels 23, 25, 27, 29,respectively. Illustratively, ports 12, 22 are corresponding input andoutput ports, i.e., they are each connected to the same terminal or datacommunications device. Similarly, ports 14, 24, ports, 16, 26 and ports18, 28 are each connected to the same device. In FIG. 1, as in all ofthe figures, the channels are schematically depicted and are not drawnto scale.

Referring now to FIG. 2, there is schematically depicted a furtherembodiment of a 4×4 star-coupler. This particular embodiment comprisesinput ports 35, 40, 45, 50 and output ports 39, 44, 49, 54 which arelocated opposite ports 35, 40, 45, 50, respectively. Input port 35 andoutput port 39 are preferably connected to the same terminal or device.Similarly, ports 40, 44, ports 45, 49 and ports 50, 54 are eachconnected to the same terminal or device. Each of the input ports isprovided with a separate channel to each of the output ports, except thecorresponding output port connected to the same device, illustratively,the output port directly opposite that input port. For example, inputport 35 is provided with channel 36 to output port 44, channel 37 tooutput port 49 and channel 38 to output port 54. In this embodiment,input port 35 is not provided with a channel to its oppositecorresponding output port, namely, port 39.

Advantageously, such a configuration wherein a star-coupler's input andoutput ports are not coupled to each other eliminates the echoencountered in conventional passive star-couplers.

FIG. 3 is a schematic illustration of another embodiment of theinvention comprising input ports 60, 65, 70, 75 and output ports 80, 85,90, 95. As in the embodiment of FIG. 1, light from any input port isprovided to all of the output ports. In this embodiment, a binary treenetwork connects all input ports to a mixing channel and a second binarytree network connects the mixing channel to all output ports.Specifically, light from input port 60 enters channel 61, then channel63 and then channel 100. From channel 100, the light is distributed tochannels 83 and 93. From channel 83, the light is distributed tochannels 81, 82 which are coupled to ports 80, 85, respectively.Similarly, from channel 93, the light is distributed to channels 91, 92which are coupled to ports 90, 95, respectively. Light input to any ofinput ports 65, 70, 75 is similarly provided to all of the output ports80, 85, 90, 95.

Referring now to FIG. 4, there is depicted a perspective view of thedevice schematically illustrated in FIG. 1. This 4×4 star-couplercomprises a first section 110 and a mating second section 120.Illustratively, these sections are mirror images of each other and eachforms one half of the star-coupler.

Each of sections 110 and 120 is preferably fabricated by injectionmolding and comprises a block-like structure having a planar face 112,122, respectively. A network of channels, preferably semicircular inshape, is formed in each of these faces 112, 122. The configuration ofthis network has been described in conjunction with FIG. 1.

Attachment of section 110 to section 120 thus provides a network ofcircular channels in which each input port is connected to all of theoutput ports. Each input port and each output port is formed by two portportions, for example 12 and 12A.

Advantageously, sections 110, 120 are each constructed from a suitableplastic optic cladding material. Further, the entire network of channelsis filled with a suitable fiber optic core material prior to attachmentof section 110 to section 120. Application of force (by means not shown)to the sections will cause excess core material to be expelled frombetween the sections. Alternatively, sections 110, 120 may first bejoined together and then core material injected into the ports toentirely fill the channels. The cladding material has a lower index ofrefraction than the core material. Thus, light is propagated in the corematerial and guided and confined therein by the cladding material.

A suitable material for the cladding is fluorinatedpolymethylmethacrylate (PMMA) while a suitable material for the core ispure PMMA.

Advantageously, the input and output ports are formed during injectionmolding and are appropriately aligned with respect to the channel(s) towhich they are attached. These ports are adapted to be easily connectedto known connectors and preferably do not require further machining. Theparticular shape and configuration of the ports depend on the nature ofthe connector to which it is to be connected.

In an alternative embodiment from that of FIG. 4, sections 110, 120 areconstructed from practically any material which can be injection molded.FIG. 5 illustrates such an embodiment in the form of a modifiedcross-sectional view of FIG. 4. In this embodiment, a suitable claddingmaterial 122 is applied to the surfaces of section 120 defining channels23, 25, 27, 29 therein. Core material is then placed within the channelsas discussed in conjunction with the description of FIG. 4.

FIG. 6 illustrates a portion of a star-coupler assembled in accordancewith the invention. Specifically, a first input port comprises halves16, 16A and core 130 while a second input port comprises halves 18, 18Aand core 132.

While it is apparent that the invention herein disclosed is wellcalculated to fulfill the objects stated above, it will be appreciatedthat numerous modifications and embodiments may be devised by thoseskilled in the art, and it is intended that the appended claims coverall such modifications and embodiments as fall within the spirit andscope of the present invention.

Specifically, a one-piece structure having a suitable network ofchannels can be formed by injection molding. Furthermore, the two matinghalves which form a star-coupler need not be mirror images of eachother, for example, one may contain a channel of more than half of thecross-sectional area of the resultant channel and the other may containless than half of the cross-sectional area or none of the resultantchannel. The channel may be non-circular. For example, for ease ofmolding operation, the channel can be a rectangular or square-walledchannel with a slight taper for mold release and so on. Moreover, theinvention is not limited to the disclosed 4×4 star-couplers, but may bepracticed with star-couplers having any practical number of ports.Additionally, injection molded fiber optic connectors may be provided tosimply connect together two optical fibers and not interconnect variousports and channels as in a conventional star-coupler.

What is claimed is:
 1. A method for constructing a star-couplercomprising the steps of:forming by injection molding a first section anda second section each having a plurality of channels therein including amixing zone, a plurality of input connector portions and a plurality ofoutput connector portions, each of said input and output connectorportions being adapted for connection to a mating fiber optic connector,being connected to at least one of said channels, and being integralwith the section in which it is molded; and said channels, inputconnector portions and output connector portions of said second sectionbeing configured so as to align and mate with said channels, inputconnector portions and output connector portions of said first section;filling said plurality of channels in each of said first and secondsections with a core material for transmitting optical signals; andfastening said first section to said second section so as to align saidchannels and said connector portions of said first section with saidchannels and said connector portions of said second section, thusforming a corresponding plurality of channels and connectors, whereinsaid step of filling may occur prior or subsequent to said step offastening.
 2. The method of claim 1 further comprising disposing a fiberoptic cladding material on said channels before said step of fillingsaid channels with said core material so as to form a cladding structurehaving a circular cross section surrounding said core material, therebyconfining and guiding optical signals transmitted within said corematerial.
 3. The method of claim 1 wherein said filling step comprisesinjecting said core material into said channels of said star-couplerafter said step of fastening.
 4. The method of claim 1 wherein saidfilling step comprises placing said core material in said plurality ofchannels in said first section and separately placing said core materialin said plurality of channels in said second section before said step offastening.
 5. A method for constructing a star-coupler comprising thesteps of:forming by injection molding a block having a plurality ofchannels therein, a plurality of input connectors and a plurality ofoutput connectors, each of said input and output connectors havinglocated therein at least one channel of said plurality of channels, saidplurality of input connectors and said plurality of output connectorsbeing integrally formed with said block and said plurality of channels,and filling said plurality of channels in said block with a corematerial for transmitting optical signals.
 6. The method of claim 5further comprising disposing a fiber optic cladding material on surfacesof said block defining said channels before said step of filling saidchannels with said core material so as to form a cladding structuresurrounding said core material, thereby confining and guiding opticalsignals transmitted within said core material.
 7. The method of claim 5wherein said step of filling comprises injecting said core material intosaid channels of said star-coupler.